1. Related Inventions
This application is related to U.S. Pat. No. 3,804,230 and co-pending application Ser. No. 552,816, now U.S. Pat. No. 3,976,177, both of which are assigned to the same assignee as the present invention. The invention is further related to apparatus for the movement of objects across its surface and more specifically, to apparatus which permit omni-directional movement of the objects in a plane defined by the surface of the apparatus.
2. Discussion of the Prior and Related Art
The referenced U.S. Pat. No. 3,804,230 describes and claims a commercially suitable apparatus having a plurality of powered rollers with drive wheels mounted in a helix on the periphery of the roller. The drive wheels comprise in part a surface upon which an object such as a pallet may be moved. As the roller is caused to rotate by an appropriate driving means, the wheels power the pallet in the direction of roller rotation. Right angle transfer can be accomplished by maintaining the roller stationary, but powering the wheels are mechanically coupled to the driving means. Clockwise or counterclockwise motion can also be accomplished through appropriate control of individual rollers.
Intermediate the rollers, a plurality of independently rotatable nonpowered elements may be positioned to provide further support for the pallet. The referenced U.S. application Ser. No. 552,816, U.S. Pat. No. 3,976,177, describes and claims a element which is particularly suitable and advantageous for this use. Briefly, the element is comprised of an axle member which defines a central axis and is rotatably mounted between a pair of support members. A plurality of lobes are individually rotatably mounted and secured to the axle member. The axis of the lobes together define a plane perpendicular to the central axis and arranged symmetrically about the central axis. In the specific case of a two lobed element, the angle between lobe axis is 180.degree.. In a three lobed element, the angle between adjacent lobe axis would be 120.degree..
The lobe surface is curved and constitutes a portion of an imaginary spherical surface. The total surface of all lobes of any particular element comprises a substantially spherical surface, permitting space sufficient between adjacent lobes to permit independent rotation. The spherical surface projects above the adjacent support members to provide a load surface for the pallets.
3. The Problem
Movement of objects on a surface defined by a plane commonly tangent to the imaginary spheres formed by the plurality of the rotatable elements is substantially omni-directional. Friction in the apparatus is substantially reduced to bearing and rolling friction. The single exception is where a particular element is positioned such that when the vector of a force applied to it by movement of the pallet is in a plane defined by the axis of the contacted lobe and axis of the axle member. This position of the element is called its "dead spot position".
Generally, the dead spot position causes no problem since the probability of an element being in this position is statistically small and neglible in effect where a large number of elements are used. In powered applications, where the elements serve as intermediate support surfaces between powered rollers, the effect of dead spot positioning is essentially minimal. There are instances, however, where it would be desireable to eliminate dead spot positioning. For example, use of rotatable elements in nonpowered applications dictate that the manual energy requirements be low. When experiencing heavy loads pallets having surface characteristics such that the coefficient of friction between pallet and the stationary lobe surface is high, it has been noted that manual movement becomes more difficult. This may become particularly evident when the number of elements supporting a heavy load is small. The wear on lobe and pallet surface in such instances becomes more pronounced.
It was with this problem in mind that applicants determined that the paramount object was to develop an apparatus which would substantially reduce the effect of dead spot positioning. The following summary demonstrates that the objective was met.